1. Field of the Invention
The present invention is directed to a method for treating stress corrosion cracking in pipes, pipelines and other tubular members and a remediation structure for reinforcement repair of the same. More particularly, the present invention is directed to a pipe restraining repair method for treating stress corrosion cracking in pipes, pipelines and other tubular members using composites and to a pipe remediation structure.
2. Background/Description of Related Art
A wide variety of devices, apparatuses, systems and methods for repairing or reinforcing members such as pipe, pipelines, and structural members are known, including, but not limited to, the disclosures in U.S. Pat. Nos. 4,700,752; 5,348,801; 5,445,848; 5,632,307; 4,676,276; 6,276,401; 6,774,066; 7,387,138; 7,426,942; 7,367,362; 7,500,494; and 7,523,764—all incorporated fully herein for all purposes.
Structural members can be degraded, i.e. physically damaged or deteriorated due to cyclic loading fatigue enhanced by corrosion, erosion, temperature fluctuations, natural causes, third party causes, and time. Degraded members often require repair and/or reinforcement to preserve and/or restore their integrity and extend their useful life. The problems resulting from damage and deterioration affect piping systems which are subject to deterioration due to several factors, including sulfate reducing bacteria, galvanic action, and third party damage. The problem is not limited to piping systems. It also affects other structures such as piling, concrete columns, petroleum storage tanks, etc. which are subject to deterioration and damage.
Typically, cracks within the wall thickness of a piping structure, once initiated, will continue to propagate (both longitudinally along the length of the pipe or inwardly thru the wall thickness) until eventually the crack has gone thru the wall thickness and the pipe is unable to remain pressure containing. Stress corrosion cracking of pipes, pipelines and other tubular members is a problem that will continue until a failure state is experienced. Depending on the contents of the pipe and the pressure conditions of the pipe, such failure could result in serious damage to property and/or life. Once a crack is formed in a pipe, the sharp tips formed at the leading edges of the crack create a stress concentration and thereby cause continued propagation of the crack due to the stress or pressure cycles present in the pipe. Left unchecked, the crack will ultimately propagate through the wall of the pipe causing catastrophic failure. Currently, there does not exist a suitable method for treating stress corrosion cracking.
Currently, one of the methods to stop/repair crack propagation is to terminate the crack by drilling a hole through the pipe at the crack tips. Doing so eliminates the sharp tip and stress concentration thereby mitigating the propagation of the crack. The holes are then filled or patched. However, this method is unacceptable because it cannot be employed on pressurized pipe and it creates further potential for hazardous conditions in that creating such drilled holes in the pipe will cause temporary leakage of the contents of the pipe thereby creating environmental hazards during the repair when the pipe contains hazardous materials. Often with stress corrosion cracking there exists a plurality of cracks around the outer diameter of the pipe in the pipe repair zone; thus, the drilling technique is further unsuitable because it demands creation of a plurality of holes in the pipe in the pipe repair section.
Similarly, another current method for repairing stress corrosion in piping is to terminate the crack by grinding the cracked area while still having sufficient remaining wall thickness to make a secondary repair with either a welded split sleeve or a composite system. However, grinding the crack removes wall thickness which can weaken a pipe.
Another existing method for treating stress corrosion cracking in pipe includes placing the damaged pipe section (crack) in compression using mechanical compression devices. These methods typically employ very heavy metal clamps using a mechanical advantage of bolts to provide the compressive force. The compressive force prevents pipe movement (the opening and closing of the crack) during pipe pressure cycles thereby preventing further propagation of the crack. These methods are very expensive creating unfavorable economic and logistical repair conditions.
Yet another, but still unsatisfactory repair option, is to cut out (remove) the damaged section of pipe and splice (replace) in a new section. This creates a requirement for shutting down all flow through the pipe, a condition that could have severe economic impact (in shutting down the processes using the pipe) as well as environmental impact in dealing with the contents of the pipe once the damaged section is removed.
Older methods of repairing damaged pipelines comprise the replacement of the damaged or defective pipe section with new pipe or the installation of a metal sleeve over the damaged or defective area. Depressurizing the pipe or putting the pipe out of service while the pipe replacement is performed is often required for these known pipe repair methods. This procedure can become costly and inconvenient for the pipeline owner as well as the general public.
Also, Pipe Wrap, L.L.C. (Houston, Tex.) provides existing “Leak Stop™” methods for patching a leaking pipe by bonding a gasket material to the underside of a cured fiberglass material to create a patch, and then clamping this patch over the leak using banding devices known in the art. An epoxy putty is then spread over the entire repair zone, a corrosion coating/primer/adhesive is applied to the repair zone and a low tensile strength (4,900 psi) pipe wrap material is then wrapped over the setting epoxy before the epoxy is fully cured. The patch serves to provide a seal gasket over the hole(s) in the pipe (pipe wall loss damage is caused by presence of the holes) to stop the leaking, but not strengthen the pipe, and also serves to distribute the compressive load applied by the bands so as to prevent the damaged pipe walls from collapsing. However, this method is not suitable for addressing and arresting stress corrosion cracking, nor can it be used with temperatures exceeding 300° F., cryogenic temperatures or pipe pressures exceeding 150 psi owing to the limitations of the gasket seal. Further, the bands cannot be tensioned to their upper limits as doing so would collapse the damaged pipe.
Advances in composite materials and methods in the past two decades have introduced composites as a more widely accepted repair method for piping and infrastructure rehabilitation. Composites have offered owners of pipelines a cost-effective alternative to the disruption of service caused by pipe replacement or steel sleeves because composite repairs can be applied to the damaged areas while the pipeline is still in operation.
With the discovery of nanoparticles, it has been scientifically shown under laboratory conditions that the physical properties of a matrix and/or composite material such as tensile strength, tensile modulus, thermal and electrical conductivity, toughness, durability, etc., are enhanced with the incorporation of nanoparticles such as but not limited to nanotubes, graphene, nanofibers, bucky balls, nano clays, etc. (collectively “nanoparticles”). For example, it is known in the art that in the laboratory, epoxies have been impregnated with nanoparticles to form a hardened material. A matrix, in this sense, is generally understood to be defined as a pre-cured material, liquid or molten state that may include for example, but is not limited to, polyester resin, vinyl ester resin, epoxy resin, polyethylene, polypropylene, nylon, rubber, and the like. The composite material may generally be defined as any material that incorporates a fiber or aggregate that increases the resultant material's “load carrying” capability.
Known pipe repair and reinforcement systems include a fabric impregnated with a moisture-curing polyurethane polymer system or a fabric impregnated with a resin polymer in the field during installation of the product or a cured pre-form that is bonded with an adhesive as it is wrapped around a member. These products provide reasonable performance and service life. However, there is a need for improved performance especially in the area of extended fatigue/service life.
Permanence of a Fiber Reinforced Polymer, “FRP” composite repair is a requirement for pipeline repair methods under current DOT regulations (49 CFR §§192, 195; incorporated fully herein). The question of permanence of some FRP composite repairs has become of great concern to pipeline owners due to delaminations due to fatigue of some composite systems.
Consequently, these failed FRP's have provided questionable permanent repairs. DOT has ruled that FRP repairs are temporary unless the pipe is repaired by a method that reliable engineering tests and analyses show permanently restores the serviceability of the pipe.
As such, there remains an existing need to provide an acceptable method for repairing corrosion stress cracking in pipes, pipelines and other tubular members, and a suitable reparation or remediation structure.